1. Field of the Invention
The present invention relates to encapsulation compositions in which an encapsulate is encapsulated in a glassy matrix. More particularly, the present invention relates to flavor encapsulation compositions in which a flavoring agent is encapsulated in a glassy matrix.
2. Discussion of the Background
The encapsulation of encapsulates is an area of active research. In particular, the encapsulation of encapsulates such as medications, pesticides (including insecticides, nematocides, herbicides, fungicides, microbicides, etc.), preservatives, vitamins, and flavoring agents is desired for a number of reasons. In the case of medications and pesticides, such encapsulation may be desired to achieve the controlled release of the medication or pesticide. In the case of vitamins, the encapsulation may be carried out to protect the vitamin from air-oxidation and, thus, to extend the shelf life of the vitamin. In the case of a flavoring agent, the encapsulation may be carried out to place the flavoring agent in an easily metered form which will release the flavoring agent at a controllable event, such as the addition of water.
It is generally known to skilled practitioners in the field of flavor encapsulation that current practical commercial processes leading to stable, dry flavors are generally limited to spray drying and extrusion fixation. The former process requires the emulsification or solubilization of the flavor in a liquid carrier containing the encapsulating solids, followed by drying in a high temperature, high velocity gas stream and collection as a low bulk density solid.
While spray drying accounts for the majority of commercial encapsulated materials, several limitations of the process are evident. Low molecular weight components of complex or natural flavor mixtures may be lost or disproportionate during the process. The resultant flavor-carriers are porous and difficult to handle. In addition, deleterious chemical reactions such as oxidation can result on surfaces exposed during and after drying. The final product, a dry, free flowing powder, will release the encapsulant rapidly upon rehydration whether rapid release is desired or not.
U.S. Pat. No. 3,971,852, to Brenner et al., teaches the use of modified starch, gums and other natural hydrocolloids with lower molecular weight polyhydroxy compounds to yield a glassy cellular matrix with encapsulated oil at a maximum of 80 volume %. This system forms a shell surrounding the oil flavoring but is limited to lipophilic flavoring agents. Saleeb and Pickup, in U.S. Pat. No. 4,532,145, describe a process and composition in which a volatile flavorant is fixed by spray drying from a carrier solution made up of 10-30% of a low molecular weight component such as a sugar or an edible food acid with the balance of solids being a maltodextrin carbohydrate in the amount of 70-90%. U.S. Pat. No. 5,124,162, to Boskovic et al., discloses a carrier mixture composed of mono- and disaccharides (22-45%), maltodextrins (25-50%), and a high molecular weight carbohydrate such as gum arabic, gum acacia or chemically modified starch (10-35%) to which flavoring agents are added and the subsequent solution spray dried to yield a free flowing powder with a bulk density of 0.50 g/cc.
Several technical issues unmet by these approaches cited are evident. Firstly, thermally sensitive flavors undergo undesirable reactions, including oxidations, rearrangements and hydrolyses. Secondly, volatile components are lost during the atomization and evaporation in the dryer.
A second process route, that of melt encapsulation, has been utilized to advantage with lipid-based flavors. In this technology a melt is prepared in the form of a high solids carbohydrate syrup, flavoring oils with emulsifier are added under pressure, agitated, and dispersed, and the mixture is injected into a chilling, dehydrating solvent bath to obtain fine, rod-like filaments. After the solvent removal, the matrix is reduced in size and, in some cases, coated with anti-caking agents before being packed. Description of the key parameters of this process can be found in the U.S. Pat. Nos. 2,809,895 and 3,0410,180, to Swisher, U.S. Pat. Nos. 2,856,291 and 2,857,281, to Shultz, U.S. Pat. No. 3,704,137, to Beck, and subsequent improvements in the art are detailed in U.S. Pat. No. 3,314,803 for encapsulation of volatiles such as acetaldehyde.
An alternative route to encapsulating flavorings is taught by Sair and Sair, in U.S. Pat. No. 4,230,687. In this approach, high molecular weight carriers such as proteins, starches or gums are plasticized by addition of water in the presence of the encapsulate and subjected to a high shear dispersive process. The dispersed matrix plus encapsulate is then recovered and dried to yield a stable product.
Another alternative process, melt extrusion, can be utilized for flavor fixation and encapsulation. In this process, a melting system, i.e. an extruder, is employed to form the carrier melt in a continuous process. The encapsulate flavor is either admixed or injected into the molten carbohydrate carrier. Saleeb and Pickup teach, in U.S. Pat. No. 4,420,534, use of a matrix composition consisting of 10 to 30 wt % of a low molecular weight component chosen from a series of mono- or disaccharides, corn syrup solids, or organic acid with the balance of the mixture being maltodextrin. The matrix base is dry blended with an anhydrous liquid flavoring component and melted in a single screw extruder to yield a solid matrix characterized as a glass with a glass transition temperature &gt;40.degree. C.
Levine and Slade, in U.S. Pat. Nos. 5,087,461 and 5,009,900, teach a similar approach utilizing a composition consisting of a modified food starch, maltodextrin, polyol, and mono- and disaccharide components. The starch is a chemically modified, water-soluble starch and is used in an amount of 40 to 80% of the total mixture. The balance of the composition is comprised of 10-40% of maltodextrin, 5 to 20% of corn syrup solids or polydextrose and 5-20% of mono- or disaccharide. This matrix is made to balance processing response with glass matrix character.
In the two preceding examples in the '461 and '900 patents, the matrix composition was carefully defined to accommodate the processing limitations of the extruder as well as to generate a stable matrix being in the glassy state and characterized by a glass transition temperature of &gt;40.degree. C.
Formation of a matrix in the glass state is of particular value for encapsulation of water-soluble flavorings and extracts. In these cases, the role of water as a plasticizing agent conflicts with this desired result, because water in the final product has the effect of lowering the glass transition temperature (T.sub.g) of the glassy matrix. In model studies of a number of food carbohydrate systems, the upper limit of water content is approximately 7-10 wt. % for lower molecular weight components such as mono- and disaccharides, maltodextrins and combinations of these agents. At higher water contents, the T.sub.g is lowered to the extent that the matrix is in the undesirable rubbery or plastic state at room temperature.
In order to insure higher T.sub.g 's there are several options available. By limiting the class of encapsulate materials to lipophilic materials such as citrus oils, plasticizing moisture may be removed by a boil off process as described in U.S. Pat. No. 2,809,895. Alternatively, the use of melt encapsulation as taught in U.S. Pat. No. 4,420,534 limits the flavoring agents to materials with lower vapor pressure which can be admixed to the premelt composition. In addition, flavorings which are in the form of aqueous extracts, water, and alcohol-water solutions will result in a product with a T.sub.g much below 25.degree. C. leading to plastic flow and loss of volatiles upon storage.
Similarly, in U.S. Pat. No. 5,009,900, the flavorings are limited to those with limited volatility and total moisture levels in the final product are less than 11% by weight. Many of the key topnotes and unique flavor components of complex flavors have high vapor pressures at room temperature and are not easily encapsulated by such a process.
Preparation of a solid in the glass state is dependent upon both matrix composition and the process used to generate the encapsulating material. The advantages of retaining the glass form of the matrix is increased physical stability of the solid, reduced loss of incorporated volatiles, and reduction of deleterious intermolecular reactions. A detailed discussion of the physical chemistry of water-food polymer interactions as relating to the glassy state and their transition temperatures can be found in H. Levine and L. Slade, "Glass Transitions in Foods", pgs. 83-205 in Physical Chemistry of Foods, H. Schwartzberg and R. Hartel, Eds., Marciel Dekker, New York, 1992; and H. Levine and L. Slade, "Water as a Plasticizer: physico-chemical aspects of low-moisture polymeric systems", pgs. 79-185 in Water Science Reviews, Vol. 3, F. Franks, Ed., Cambridge University Press, London, 1988, which are incorporated herein by reference. The role of water as plasticizer with food polymers, as well as the relationships between molecular composition and dynamics of interactions between various components, are discussed in these references.
Thus, there remains a need for encapsulation compositions in which an encapsulate is encapsulated in a matrix which is stable in the glass state at ambient temperatures. In particular, there remains a need for flavor encapsulation compositions in which a flavoring agent is encapsulated in a matrix which is stable in the glassy state at room temperature, i.e., has a T.sub.g sufficiently high to prevent caking and plastic flow at ambient temperatures. There also remains a need for flavor encapsulation compositions which have a high T.sub.g and are amenable for encapsulating volatile and sensitive flavor components.